The goal of this research proposal is to elucidate mechanisms which maintain the fidelity of transmembrane signal transduction. For the G protein coupled receptors, this process is made complex by the multiplicity of Gi subtypes. This proposal will focus on 1) construction and characterization of the Gi proteins which contain a substitution at the pertussis toxin modification site which will render them insensitive to pertussis toxin 2) creation of a cell which contains a single form of functional G protein 3) comparison of the G protein and effector coupling of the two splice forms of the rat striatal D2 dopamine receptor. These approaches will help to determine mechanisms which govern receptor signalling to effector systems. To date, little is known about the mechanisms which allow the high fidelity of transmembrane signal transduction in response to receptor activation. Using molecular biology techniques, G proteins which contain a mutation a the pertussis toxin site will ultimately be introduced into a permanent I clonal cell line, which after intoxication with pertussis toxin, will contain only the mutant G protein in a functional form. This approach will allow the receptor mediated effector responses to be examined in the presence of a single defined Gi subtype. These combined approaches will help to clarify the biochemical basis of signal transduction. Since dopamine is an important hormone in the periphery and a neurotransmitter in the CNS, understanding of its mechanisms of signalling could have important implications in some of the disorders thought to have a basis in i dopaminergic dysfunction, such as schizophrenia and Parkinson's disease.